Update Dockerfile
I've encountered an error while executing the Dockerfile.

- #177

You can view the Dockerfile here: [Dockerfile Link @StevenJSCF](https://github.com/StevenJSCF/OpenVoice/blob/11cdec7d98f37c142cebcc2fcb79bf7565f6a6ad/docs/DockerFile).

### Context:
I was trying to build the Docker image using the provided Dockerfile when I ran into the following error:

Here is a screenshot of the error:
![Error Screenshot](https://github.com/myshell-ai/OpenVoice/assets/49465120/8237ebaf-e9ad-4985-b536-1601c3a78ff6)

### Changes Made:
- **Base Image**: Changed to `python:3.10-slim` for a lighter and more efficient image.
- **Support for v2 Material**: Added steps to download and set up v2 checkpoints.
